1. Field of Invention
The invention relates to a method for operating a refrigerating plant.
2. Description of the Prior Art
Apart from electric power and/or mechanical energy, increasingly thermal energy in the form of warm water, hot water and steam is used for driving refrigerating machines. This thermal energy can e.g. be district heating, which is in part available in excess form in summer from heating power stations (HPSs) and block heating power stations (BHPSs). Waste heat from industrial processes or solar/geothermal energy can also be used as motive energy.
Particularly in summer the district heating thermal energy and solar energy are particularly attractive for the operation of refrigerating plants, because this energy becomes available at the precise time when cold is e.g. needed for summer air conditioning. Thermal energy is also an option for refrigerating plants operated throughout the year.
A special type of problem e.g. arises in the case of refrigerating plants operated throughout the year and which are supplied with heat from BHPSs. Other than for heating purposes in winter, in summer this heat is difficult to sell. The summer demands are largely limited in the residential and industrial areas to service water heating. However, in the case of current-carrying power-heat coupling there is necessarily an excess waste heat availability, which could be usefully paid off by means of a power-heat-cold coupling.
The temperature level in a district heating network is in winter typically 100 to 130xc2x0 C., whereas in summer it is lowered to values around 90xc2x0 C. The usable temperature level of the waste heat of internal combustion engines of a BHPS is by design typically 90xc2x0 C., apart from hot-cooled engines or pure exhaust gas utilization. These examples show that in numerous cases temperatures around 90xc2x0 C. are expected, making difficult a use for cold generation purposes.
Apart from a low efficiency with hot water, steel equipment at such low temperatures suffer from a problem which, although not unsolvable, is difficult to implement from an ecological and economic standpoint. Admittedly water/lithium bromide absorption refrigerating plants can be operated with such low temperatures, but with the low efficiency levels achieved have difficulties in providing cold water at e.g. 6xc2x0 C. Admittedly ammonia/water absorption refrigerating plants can reach temperatures below 6xc2x0 C. and even below 0xc2x0 C., but the costs are very high and the efficiency once again low. Mention is finally made of adsorption plants, which admittedly can cope with low temperatures, but are expensive to purchase, very large, heavy and also very energy-intensive.
In many hot countries the power consumption in summer is high and often higher than in winter, because the numerous electric room cooling devices lead to pronounced current peaks, which have to be expensively covered and often lead to overloading of the main supply networks. In cooler countries the power consumption in winter is admittedly high, but at the same time in the case of power-heat coupling the heat demand for heating purposes is also high and a BHPS can e.g. favorably cover the parallel energy requirement by full load operation. In summer, due to the limited heating heat requirement, a reduction of the power generation is favorable, because room cooling equipment in cool countries provide no significant contribution to the power consumption and the peaks are not or are less pronounced than in hot countries.
In both the cases described (not and cold countries), the re is consequently a wish, even though for completely different reasons, to use thermal energy in summer for operating a refrigerating plant. Winter operation with thermal energy is often impossible (no solar heat production), undesired (already existing high heating heat demand) or uneconomic (due to seasonly higher returns from heat sales for heating purposes).
The problem of the invention is to provide a method which permits a particularly economic operation of a refrigerating plant.
According to the invention this problem is solved by a thermal coupling of an electromotively and/or mechanically driven compression refrigerating plant with a thermally supplied refrigerating plant in such a way that the condenser of the compression refrigerating plant is cooled by the thermally supplied refrigerating plant. The subclaims contain advantageous developments of the invention.
Refrigerating plants with an electrical or mechanical drive are generally constructed as compression refrigerating plants. The energy requirement for driving a compressor is dependent on the evaporation and condensation temperature. As the evaporation temperature is generally fixed by the cold application, with regards to the compressor energy demand scope only exists when fixing the condensation temperature, which should be as low as possible with rising condensation temperature it is e.g. appropriate to operate with cooling water from a cooling tower, condensation of the refrigerant in an evaporative cooler or condensation with an air-cooled condenser. The use of cooling towers and evaporative coolers is being made ever more difficult or is even prohibited, because the water demands are considerable. Air cooling is the least favorable solution to the high temperature, although no water is consumed.
For a low temperature of the thermal motive energy, refrigerating plants with a thermal drive are normally absorption refrigerating plants. At the prevailing low temperatures it is difficult and/or energy-intensive, to make available usable use temperatures. At the low temperature of the thermal motive energy a high use temperature is increasingly more economic. With respect to the condensation of the refrigerant and the removal of the absorption heat the same criteria apply as in a compression refrigerating plant.
If the compression refrigerating plant is equipped with an air-cooled condenser, it can condense the refrigerant in winter at a low external temperature without cooling by the adsorption refrigerating plant in the case of low energy demand. The adsorption refrigerating plant can then be switched off or used for other purposes.
Thus, in winter the low air temperature for condenser cooling of the compression refrigerating plant reduces the electrical or mechanical energy demand thereof. The adsorption refrigerating plant can remain switched off if thermal motive energy is scarce or expensive. The adsorption refrigerating plant can also be used for other cooling or refrigerating functions if a need exists. In this case there are two autarchic refrigerating plants. In summer the adsorption refrigerating plant is operated with existing and/or inexpensive (free) thermal motive energy. The adsorption refrigerating plant serves to cool the condenser of the compression refrigerating plant, so that the electric or mechanical energy requirement of the compression refrigerating plant is low. Simultaneously the use temperature of the adsorption refrigerating plant is high, e.g. the refrigerant is condensed with an air-cooled condenser without any consumption of water. Water cooling of the condenser is obviously also possible.
The following construction is proposed for an advantageous coupling of the compression refrigerating plant condenser with the adsorption refrigerating plant. The adsorption refrigerating plant is constructed as a water cooler (for frost or corrosion protection reasons it is also possible to use another liquid, e.g. a brine, included hereinafter under xe2x80x9cwaterxe2x80x9d). The compression refrigerating plant is a bare or finned conduit condenser, the refrigerant to be condensed flowing through the pipes and the cooling air around the pipes. Fans ensure the air flow and they are conventionally exhaust fans.
With a low outside temperature (e.g. in the case of cold winter weather) the condenser of the compression refrigerating plant is cooled with external air. With high outside temperatures the compression refrigerating plant condenser is cooled with cold water from the adsorption refrigerating plant. For this purpose the compression refrigerating plant condenser is flooded with cold water from the adsorption refrigerating plant.